The invention relates to a cylinder head gasket for a multicylinder engine, in particular, for a diesel engine for a commercial vehicle. The cylinder head gasket comprises a single-layered gasket plate with a single sheet metal layer, combustion chamber openings, and for each combustion chamber opening at least one ring-shaped combustion chamber sealing element, which encloses the associated combustion chamber opening and is in the form of a sheet metal ring which is arranged on the sheet metal layer and is joined with a substance-to-substance bond, in particular by welding, to the sheet metal layer. The sheet metal layer can, however, also be provided with coatings and/or inserts.
When, in such a cylinder head gasket, a bead which is elastic in the direction of its height is provided in the sheet metal layer outside of the sheet metal ring for sealing around a combustion chamber opening, the aforementioned sheet metal ring also has the function of a so-called stopper for preventing excessive flattening of the sealing bead when installing the cylinder head gasket and while the engine is in operation. However, the present invention relates, in particular, to cylinder head gaskets in which sealing around a combustion chamber opening is effected with only one sheet metal ring, so that the latter forms the single combustion chamber sealing element. In this case, the sheet metal layer is then flat at least in the vicinity of the combustion chamber openings, but it can also be flat overall.
In known cylinder head gaskets of the kind mentioned at the outset, the sheet metal rings in the form of flat rings are arranged on that side of the sheet metal layer (usually and hereinbelow referred to as carrier sheet) which faces the cylinder head when the gasket is installed. The sheet metal rings are joined to the carrier sheet, which is flat under the sheet metal rings, by welding, namely by spot welding or by means of continuous weld seams. Within the scope of the present invention, it is, however, also conceivable to use different kinds of substance-to-substance bond such as, for example, adhesive bonding by means of a high-temperature-resistant adhesive.
Owing to the tendency to construct reciprocating internal combustion engines with increasingly high compression, the following problem is gaining more and more importance: as a result of the varying gas pressures occurring during operation of the engine, the cylinder head and its sealing surface facing the engine block are periodically arched upwards, i.e., away from the engine block, in the rhythm of the ignitions, which results in rhythmic sliding movements between the cylinder head sealing surface and the cylinder head gasket—such relative movements as occur in the plane of the so-called sealing gap between the sealing surfaces of cylinder head and engine block are referred to as sliding movements. It has been found that in the known cylinder head gaskets described hereinabove, these increased sliding movements can result in destruction of welded joints, but, above all, of the sheet metal rings themselves. In the latter case, a portion of a sheet metal ring facing the carrier sheet remains adhered to the carrier sheet, while, at least in the area of segments of the sheet metal ring, upper portions of the sheet metal ring are split off, which, as a consequence, can also lead to radial breakages in the sheet metal ring. At any rate, the sealing around the combustion chamber opening concerned is then no longer ensured.
The following is also to be noted in conjunction with the risk of destruction discussed hereinabove: on the one hand, the material of the weld points or weld seams serving to attach the sheet metal rings often projects above the sheet metal rings, albeit only slightly, and, on the other hand, the material that is melted on and then solidifies during the welding forms hard “weld cores”, which, when the cylinder head gasket is assembled and pressed, are subjected to high pressing forces and are thereby pressed in the direction towards the interior of the carrier sheet. Primary damage to the cylinder head gasket at the interfaces between the weld cores and the sheet metal rings can already occur at this stage, and this primary damage further increases the risk of destruction of the welded joints and/or the sheet metal rings when, after installation of the cylinder head gasket, the sheet metal rings are pressed against the cylinder head and are subjected to the sliding movements between the cylinder head sealing surface and the cylinder head gasket while the engine is in operation.